What type of sounds do frequencies in speech typically represent?

Frequencies in speech typically represent complex sounds, which are made up of multiple frequencies occurring simultaneously. Human speech is characterized by a combination of fundamental frequencies and harmonics, as well as formants, which are the resonant frequencies of the vocal tract that shape the sounds of vowels and consonants.

Unlike pure tones, which consist of a single frequency or sinusoidal waveform, or simple sinusoids, which also represent single-frequency waves, speech sounds contain rich spectral properties due to the vibrations of the vocal cords and the filtering effects of the vocal tract. Additionally, while white noise encompasses a wide range of frequencies and is perceived as a hissing or static sound, it does not replicate the structured and patterned nature of speech sounds. Therefore, the appropriate representation of speech is found in complex sounds, making that the correct choice.